A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.
The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate. A lithographic apparatus which uses EUV radiation, being electromagnetic radiation having a wavelength within the range 4-20 nm, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may for example use electromagnetic radiation with a wavelength of 193 nm).
Electrostatic clamps may be used in lithographic apparatuses operating at certain wavelengths, e.g. EUV, since at these wavelengths, certain regions of the lithographic apparatus operate under vacuum conditions. An electrostatic clamp may be provided to electrostatically clamp (i.e. hold) an object, such as a mask or a substrate (wafer) to an object support, such as a mask table or a wafer table, respectively.
The voltage which is applied to an electrostatic clamp may be considerable. For example, the voltage may be of the order of kilovolts. An insulating barrier is conventionally located over an electrode of an electrostatic clamp, the insulating barrier acting to insulate an object such as a substrate from the voltage applied to the electrode.
It is desirable to provide, for example, an apparatus and method which obviates or mitigates one or more of the problems of the prior art, whether identified herein or elsewhere.